1. Field of the Invention
The present invention relates to thermal ink-jet (TIJ) technology, and more particularly, to a method for fabricating a monolithic fluid injection device.
2. Description of the Related Art
The conventional fabrication technique of a monolithic fluid injection device typically includes standard integrated circuit (IC) technology and micro-electro-mechanical system (MEMS) technology for both front-end and back-end processes. The front-end process comprises formation of wafer driving circuits and heating elements in an IC foundry. The subsequent back-end process forms fluid chambers and orifices on said wafer in a MEMS foundry.
Both the IC and MEMS processes require one or several thin-film processing techniques, such as metal deposition, dielectric deposition, or etching of dielectric openings. Production costs and the probability of defects, however, increase with repeated thin-film processes.
Conventionally, a monolithic fluid injection device with various components, such as a fluid chamber, a heater, a driving circuit, and an orifice, is formed on a silicon wafer using a MEMS process without requiring packaging and thus results in higher yield and lower cost.
FIGS. 1A and 1B are schematic illustrations of a conventional monolithic fluid injection device fabrication process, wherein FIG. 1A shows the front-end IC process and FIG. 1B shows the back-end MEMS process. Referring to FIG. 1A, a substrate 10 (e.g., silicon wafer) having a first surface and a second surface is provided, and a monolithic fluid injection device is formed thereon. In a typical processing sequence, a patterned sacrificial layer 20 is formed on the first surface of the substrate 10. A patterned structure layer 30 is formed on the first surface of the substrate 10 and covers the patterned sacrificial layer 20. A patterned resistive layer 40 is formed on the structure layer 30 as a heater. A patterned insulating layer 50 having a heater contact opening 45 is formed over the structure layer 30. A patterned conductive layer 60 is formed overlying the structure layer 30 and fills the heater contact opening 45 as a signal transmitting circuit 62. A patterned protective layer 70, having a signal transmitting circuit contact opening and covering the insulating layer 50 and the conductive layer 60, is formed overlying the substrate 10.
Referring to FIG. 1B, the IC processed wafer is then subjected to wet etching. A fluid channel 80 is formed in the second surface of the substrate 10 and exposes the sacrificial layer 20. The sacrificial layer 20 is then removed to form a fluid chamber 90. Thereafter the protective layer 70, the insulating layer 50, the structure layer 30, an orifice 90 connecting the fluid chamber 95 are formed sequentially by lithographic etching. Thus, formation of a monolithic fluid injection device is complete.
The above described formation of the orifice 90 minimally requires etching of the protective layer 70, the insulating layer 50, and the structure layer 30. The front-end process, however, also requires etching of the protective layer 70 and the insulating layer 50 to form an electrical connection between the signal transmitting circuit 62 and the heater 40 to form a signal transmitting contact.
A monolithic fluid injection device combining IC and MEMS processes is disclosed in U.S. Pat. No. 6,102,530. In this method, a structure layer is suspended over the fluid chamber; hence, the process must be precisely controlled to improve production yield and reliability.